Estimating genetic parameters of architectural and reproductive traits in young macadamia cultivars

Toft, Benjamin D.; Alam, Mobashwer; Topp, Bruce

doi:10.1007/s11295-018-1265-x

Cited by 19 publications

(20 citation statements)

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“…Raceme length had a direct influence on yield and a strong indirect influence through nut number. Raceme number and length were well-correlated (r = 0.55; P < 0.001) (Table 2), which may suggest a common gene expression mechanism that influences both axillary release (raceme number) and resource allocation to racemes (raceme length) (Toft et al, 2018). This mechanism could possibly continue to allow more assimilates to be directed toward racemes for improved nut production, retention, and yield.…”

Section: Discussionmentioning

confidence: 93%

Phenotypic Association of Multi-scale Architectural Traits with Canopy Volume and Yield: Moving Toward High-density Systems for Macadamia

Toft¹,

Alam²,

Wilkie³

et al. 2019

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Additional index words. path analysis, plant architecture, planting density, intensification, vigor, productivity Abstract. The vigorous growth and large canopy size of commercial macadamia (Macadamia integrifolia, M. tetraphylla, and hybrids) cultivars generally restricts macadamia orchards to low-density planting. Little is known of the detailed interactions between plant architecture and yield components specific to macadamia. This chapter examines how dependent traits such as canopy size and yield might be determined by direct and indirect interactions between traits at different scales within the canopy. Fifteen genotypes (n = 3) were phenotyped in two growing seasons for architectural and reproductive traits, around the age of their transition from juvenility to maturity. Genotypes varied in canopy volume, cumulative yield, and canopy efficiency, and particular genotypes with low canopy volume and high yield were considered potentially useful for future high-density orchard systems. There was high variability in architectural, floral, and yield traits at multiple scales. Direct and indirect effects of architectural traits on the variability of yield and tree size were quantified using path coefficient analysis. Canopy volume was subject to positive direct effects from trunk cross-sectional area (TCA; 0.72), lateral branching (0.24), and branch unit (BU) length (0.24). Other traits showed significant indirect effects with canopy volume via TCA, such as branch cross-sectional area (BCA; 0.43), BU length (0.40), lateral branching (0.35), and internode length (0.32). Branch angle had a significant indirect negative effect on canopy volume via BU length (L0.11). Nut number had the strongest direct effect on yield (0.97), and this relationship was significantly indirectly influenced by raceme number (0.47), raceme length (0.50), nut number per raceme (0.33), canopy volume (0.37), and branch angle (0.35). In these relatively young trees, early yield was directly and positively influenced by canopy volume (0.12), presumably due to increased early light interception, which suggests that early canopy vigor contributes to early yield. This study suggests that yield and canopy size are determined by complex phenotypic interactions between architectural traits at different scales. Therefore, preplanting (i.e., scion and rootstock selections) and postplanting (i.e., pruning and training) manipulations that specifically manage architectural traits such as shoot length, branching, branch angle, raceme length, and nuts per raceme may result in the creation of efficient macadamia canopies.

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Section: Discussionmentioning

confidence: 93%

Phenotypic Association of Multi-scale Architectural Traits with Canopy Volume and Yield: Moving Toward High-density Systems for Macadamia

Toft¹,

Alam²,

Wilkie³

et al. 2019

horts

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“…Reduced tree size is also an important selection trait to increase planting density and subsequent yield per hectare (29,30). Trunk circumference (TC) or trunk cross-sectional area can be used as an estimate of tree size in macadamia (30).…”

Section: Introductionmentioning

confidence: 99%

Genome-wide association studies for yield component traits in a macadamia breeding population

O’Connor

Hayes

Hardner

et al. 2019

Preprint

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Background: Breeding for new macadamia cultivars with high nut yield is expensive in terms of time, labour and cost. Most trees set nuts after four to five years, and candidate varieties for breeding are evaluated for at least eight years for various traits. Genome-wide association studies (GWAS) are promising methods to reduce evaluation and selection cycles by identifying genetic markers linked with key traits, potentially enabling early selection through marker-assisted selection. This study used 295 progeny from 32 full-sib families and 29 parents (18 phenotyped) which were planted across four sites, with each tree genotyped for 4,113 SNPs. ASReml-R was used to perform association analyses with linear mixed models including a genomic relationship matrix to account for population structure. Traits investigated were: nut weight (NW), kernel weight (KW), kernel recovery (KR), percentage of whole kernels (WK), tree trunk circumference (TC), percentage of racemes that survived from flowering through to nut set, and number of nuts per raceme. Results: Seven SNPs were significantly associated with NW (at a genome-wide false discovery rate of <0.05), and four with WK. Multiple regression, as well as mapping of markers to genome assembly scaffolds suggested that some SNPs were detecting the same QTL. There were 44 significant SNPs identified for TC although multiple regression suggested detection of 16 separate QTLs. Conclusions: These findings have important implications for macadamia breeding, and highlight the difficulties of heterozygous populations with rapid LD decay. By coupling validated marker-trait associations detected through GWAS with MAS, genetic gain could be increased by reducing the selection time for economically important nut characteristics. Genomic selection may be a more appropriate method to predict complex traits like tree size and yield.

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“…These findings do not reflect the phenotypic ranges observed in the current study (RL 3.6-32.3 cm, NPR 1-10.4), which may be explained by different germplasm, environments and slightly different measuring techniques. RL was moderately heritable in the current study (h 2 = 0.49), which concurred with a previous study of 15 young (4-5 years since planting) cultivars (H = 0.68), despite their estimate of heritability including non-additive genetic variance (Toft et al 2018). Heritability of NPR was lower (0.17) than expected in the current study, based on the phenotypically-observed consistency of nuts per cluster within a tree, but was similar to an estimate of broad-sense heritability by Toft et al (2018) (H = 0.11).…”

Section: Variability and Heritability Of Yield And Yield Component Trsupporting

confidence: 92%

“…KR was also highly heritable in hazelnut, where narrowsense heritability, estimated through regression of offspring means on mid-parent values, was 0.87 (Yao and Mehlenbacher 2000). The estimated narrow-sense heritability for NW and KW in this study (0.66 and 0.51, respectively) was lower than broad-sense heritability estimates of these traits in another macadamia population (0.64 and 0.66, respectively) (Hardner et al 2001), and much higher than that estimated for another population (broadsense H = 0.27) (Toft et al 2018). In comparison with the current study, heritability for NW and KW was similar in hazelnut (0.63 and 0.67, respectively) (Yao and Mehlenbacher 2000), and slightly lower than that in walnut (NW 0.86, KW 0.87) (Hansche et al 1972), where both studies calculated heritability by regressing means of offspring on the average parent value.…”

Section: Variability and Heritability Of Yield And Yield Component Trcontrasting

confidence: 60%

“…With the focus turning towards smaller trees with high yields, planting densities, and, consequently, yield per hectare, are likely to increase (Toft et al 2019). Trunk circumference (stem girth) or trunk cross-sectional area, are easily-measured traits commonly used as an estimate of tree size (Hardner et al 2002;Toft et al 2018); trunk size may affect nut yield due to uptake of resources available for growth and fruit production.…”

Section: Introductionmentioning

confidence: 99%

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Selection strategies to improve yield in macadamia using component traits and genomics

O’Connor¹

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Macadamias (Macadamia integrifolia, M. tetraphylla, and their hybrids) are native to the east coast of Australia, and are grown commercially around the world for their high quality edible nut kernel. Breeding new cultivars for high nut yield is a lengthy and laborious process that can take over two decades. Evaluations are time-consuming due to the long juvenile period of four or more years, and the low correlation between young and mature tree yield means that at least eight years of evaluations are required. Furthermore, yield has low heritability, and the large tree size necessitates low field planting density, and thus increases land use and evaluation costs. It is hypothesised that genetic gain for yield may be increased, compared to traditional breeding approaches, through the use of strategies including (i) indirect selection using yield component traits, (ii) marker-assisted selection and (iii) genomic selection. This thesis employed an experimental population of 295 seedling progeny and their 29 parents, at four sites across southeast Queensland, that were genotyped for 4,113 SNPs and 16,171 silicoDArT markers detected using Diversity Arrays Technology (DArT) methods. Population structure, genetic diversity and linkage disequilibrium (LD) between SNP markers was quantified to inform subsequent genomics analysis. LD decay was initially rapid at short distances (r 2 = 0.124 for SNPs within 1 kb of each other), but low level LD persisted for long distances. The seedling population was relatively genetically diverse (HE = 0.255), and very similar in diversity to that of the 29 parents (0.250). Furthermore, progeny with M. integrifolia x M. tetraphylla ancestry were more genetically diverse (HE = 0.278) than M. integrifolia seedlings (HE = 0.189). Progeny were moderately differentiated and clustered into three distinct groups, which represented M. integrifolia germplasm and two hybrid groups. Flowering and nut characteristics, tree growth and yield were measured on each tree. Estimations of trait heritability and genetic correlations between each component trait and yield were used to calculate selection efficiency of indirectly selecting for yield using component traits. Kernel recovery, an economically important trait, had high heritability (h 2 = 0.76) but was negatively genetically correlated with yield (rg =-0.27). Trunk circumference correlated strongly with yield (rg = 0.72) and was moderately heritable (h 2 = 0.44); however, a breeding aim is to reduce tree size without compromising yield. No component traits were appropriate or effective for indirectly selecting for high yield.

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Estimating genetic parameters of architectural and reproductive traits in young macadamia cultivars

Cited by 19 publications

References 20 publications

Phenotypic Association of Multi-scale Architectural Traits with Canopy Volume and Yield: Moving Toward High-density Systems for Macadamia

Phenotypic Association of Multi-scale Architectural Traits with Canopy Volume and Yield: Moving Toward High-density Systems for Macadamia

Genome-wide association studies for yield component traits in a macadamia breeding population

Selection strategies to improve yield in macadamia using component traits and genomics

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